1. Field of Invention
This invention relates to apparatus for compressing and conveying fluids, and with regard to certain more specific features, to apparatus which are used as compressors in compression-evaporation cooling equipment.
2. Description of Prior Art
Heretofore, nearly all refrigeration and air-conditioning compressors which have found widespread and practical application, required many moving parts. Reciprocating, rotary, and centrifugal compressors, to name a few, all have numerous moving parts. Each of these compressors will consume a portion of energy which serves only to move its parts against their frictional forces, as well as to overcome their inertia. This energy is lost in overcoming the mechanical friction and inertia of the parts, and cannot contribute to the actual work of gas compression. Therefore, the compressor's efficiency suffers. Moving parts also reduce dependability and increase the cost of operation, since they are subject to mechanical failure and fatigue. Consequently, both the failure rate and the energy consumption of a compressor tend to increase as the number of moving parts increases.
Typical refrigeration and air-conditioning compressors must use oils to reduce the friction and wear of moving parts. The presence of oils in contemporary compressors presents many disadvantages. Compressors that need oil for their operation will allow this oil to mix with the refrigerant. The circulation of this oil through the refrigeration cycle will lower the system's overall coefficient of performance, thus increasing the system's energy consumption. As such, the issue of oil-refrigerant mixtures places a restraint on ideal system design.
Another disadvantage of oil-refrigerant mixtures relates to the development of new refrigerants. Non-ozone depleting refrigerants must be developed to replace the chlorofluorcarbon (CFC) family of refrigerants. For a new refrigerant to be considered successful, it must be compatible with compressor oils. Oil compatibility is the subject of performance and toxicity tests which could add long delays to the commercial release of new refrigerants. Hence, the presence of oils in refrigeration and air-conditioning compressors reduces system efficiency and slows the development of new refrigerants.
In general, much effort has been exerted to design pumping a apparatus which lack these traditional moving parts and their associated disadvantages.
Some of these efforts have produced pumps which seek to operate on the pumped medium, using non-mechanical means. Typically these pumps operate by pressurizing the pumped medium using heat, or by exciting the pumped medium by inertia-liquid-piston effects.
Of particular interest is the inertia-liquid-piston type pump of U.S. Pat. No. 3,743,446 to Mandroian, Jul. 3, 1973, which claims to provide a pump whose pumping action is due to the properties of standing acoustical waves. Although the above patent can provide a pumping action, it does not exploit certain modes of operation which can provide greater pressure differentials and improved efficiency. As such, the Mandroian patent does not provide a practical compressor for high pressure applications, such as refrigeration and air-conditioning systems.
Another example is shown in U.S. Pat. No. 3,397,648 to Henderson, Aug. 20, 1968. Therein is disclosed a chamber in which a gas is heated and subsequently expelled through an egress check valve. As the chamber's remaining gas cools the resulting pressure differential causes more gas to be drawn into the chamber through an ingress check valve. This same method is employed in U.S. Pat. No. 3,898,017 to Mandroian, Aug. 5, 1975.
Seldom have any of the above mentioned pumping methods been applied to the field of refrigeration and air-conditioning. One such attempt is seen in U.S. Pat. No. 2,050,391 to Spencer, Aug. 11, 1936. In the Spencer patent, a chamber is provided in which a gaseous refrigerant is heated by spark discharge, and subsequently expelled through an egress check valve, due to the resulting pressure increase. As the chamber's remaining gas cools, the resulting pressure differential causes more gas to be drawn into the chamber through an ingress check valve. This approach results in ionization of the refrigerant, and could cause highly undesirable chemical reactions within the refrigeration equipment. For a practical refrigeration system, such chemical reactions would be quite unsatisfactory.
It is apparent that oil-free refrigeration and air-conditioning compressors, which require few moving parts, have not been satisfactorily developed. If such compressors were available, they could simplify the development of new refrigerants, and offer improved dependability and efficiency, thereby reducing energy consumption.
Such an oil free compressor is the subject of U.S. Pat. No. 5,020,977 to Lucas. FIG. 1 illustrates the device of Lucas which has a chamber, an input port and an output port. Forming one wall of the chamber is a transducer comprising a flexible metallic diaphragm, which has a coil attached thereto and which encircles the end of a stationary cylindrical magnet. The coil of transducer is energized through wires by a generator, which causes the coil to be driven by a periodic waveform, which in turn sets up an oscillating magnetic field about coil. Due to the alternating polarity of this oscillating field, the coil-diaphragm assembly is alternately repulsed and attracted by the cylindrical magnet and thus the diaphragm vibrates at a frequency which causes a traveling wave to be generated in the medium in the chamber. This traveling wave hits the far wall of the chamber and is reflected back out of phase with the initial wave. The chamber acts as a resonant cavity and will have a standing wave pattern set up in it. The reflected wave when it reaches the diaphragm wall is reflected coincident with the initial wave. Thus a standing wave pattern is set up in the chamber, which has pressure antinodes or displacement nodes at end wall 30 and at point 34, and pressure nodes or displacement antinodes at diaphragm 16 and at point 32.